The U.S. government tightened airline security as it searches for answers to how a 23-year-old Nigerian man eluded extensive systems intended to prevent attacks like his botched Christmas Day effort to blow up a Northwest flight from overseas.

Umar Farouk Abdulmutallab, who claimed ties to Al Qaeda, was charged Saturday with trying to destroy a Detroit-bound airliner, just a month after his father warned U.S. officials of concerns about his son's religious beliefs.

Airports worldwide tightened security days after the passenger tried to detonate a device that contained a high explosive on a flight into Detroit. After that attack, passengers have had to contend with extra pat-downs before boarding, staying in their seats without blankets or pillows for the last hour of the flight and more bomb-sniffing dogs.

Aides to President Barack Obama are pondering how terror watch-lists are used after the botched attack, according to officials who described the discussions Saturday on the condition of anonymity so as not to pre-empt possible official announcements.

These adjustments came after the Justice Department charged that Abdulmutallab willfully attempted to destroy or wreck an aircraft; and that he placed a destructive device in the plane.

An affidavit said he had a device containing a high explosive attached to his body. The affidavit said that as Northwest Flight 253 descended toward Detroit Metropolitan Airport, Abdulmutallab set off the device — sparking a fire instead of an explosion.

According to the affidavit filed in U.S. District Court in Detroit, a preliminary analysis of the device showed it contained PETN, a high explosive also known as pentaerythritol. This was the same material convicted shoe bomber Richard Reid used when he tried to destroy a trans-Atlantic flight in 2001 with explosives hidden in his shoes.

The investigation stretched to London, where a government official said border agents blocked an attempt by Abdulmutallab to return to Britain earlier this year. The suspected bomber was refused a student visa in May because authorities suspected that the school he said he was studying with wasn't genuine, the official said. He spoke anonymously because he wasn't authorized to release the information on an official basis.

The use of bogus schools to secure student visas has been identified as a weakness in Britain's immigration system. In April, one of several suspected terrorists arrested in raids in northern England was found to have a visa issued with the help of a fake college, prompting opposition lawmakers to call for a crackdown. Some 2,000 schools have closed.

On Saturday, officers from the Metropolitan Police, the force involved in most of the major terrorism investigations in Britain, cordoned off the street outside a white stone apartment block in a well-to-do area of central London. A police spokeswoman said the force was carrying out searches in connection with the incident in Detroit.

University College London said Abdulmutallab was enrolled at the school from September 2005 to June 2008. In Nigeria, the father of Abdulmutallab said his son had been a student in London, but had left the city to travel.

U.S. authorities told The Associated Press that in November, his father, a prominent banking official in Nigeria, went to the U.S. embassy in Abuja, Nigeria, to discuss his concerns about his son's religious beliefs.

One U.S. government official said the father did not have any specific information that would put his son on the "no-fly list" or on the list for additional security checks at the airport.

A Nigerian newspaper, ThisDay, said Abdulmutallab began to show his increasingly radical views on Islam during his high school days at the British International School in Lome, Togo. His attendance at the elite college preparatory school, attended by children of diplomats and wealthy Africans, could not be confirmed by school officials on Sunday.

But Efemena Mokedi, remembered Abdulmutallab from their days on the basketball team at the exclusive school as "a smart kid" and "a friendly person."

"He was a very religious person, a very honest person. He was friends with all the teachers," said Mokedi, who now lives in the United States, in an interview broadcast on the BBC. "Yes, I'm very surprised. ... This is really out of how he is as a person. This is unexpected ... He's a very good guy, a very good chap."

ThisDay, the newspaper, said Abdulmutallab left London at some point to move to Egypt, then Dubai. The government in Dubai could not immediately confirm he visited that country. A security official in Egypt said there were no records to indicate Abdulmutallab entered Egypt or had any connection to Egypt.

The security official spoke on condition of anonymity because he was not authorized to comment on the issue.

The Nigerian newspaper says that is was during his time in Dubai that Abdulmutallab began to distance himself from his family, telling them he did not want anything to do with them. The newspaper said Abdulmutallab's father lost contact with him last November, when he may have left London, according to the newspaper.

The newspaper also reported that Abdulmutallab's father is married to a woman of Yemeni descent. Yemeni officials could not immediately verify this.

Abdulmutallab appeared on the Terrorist Identities Datamart Environment database maintained by the U.S. National Counterterrorism Center, said a U.S. official who received a briefing and spoke on condition of anonymity to discuss the ongoing investigation. Containing some 550,000 names, the database includes people with known or suspected ties to a terrorist organization. However, it is not a list that would prohibit a person from boarding a U.S.-bound airplane.

The effects of the botched attack could be felt by passengers on many international flights departing from airports around the world.

Passengers getting off flights from overseas reported being told that they couldn't get out of their seat for the last hour of their flight. Air Canada also said that during the last hour passengers won't be allowed access to carryon baggage or to have any items on their laps.

The extra vigilance compounded delays in a busy holiday travel period marked by snowstorms in the Midwest and heavy rain in the East.

The TSA security directive applied to U.S.-bound flights from overseas, according to a transportation security official who spoke on condition of anonymity because the official was not authorized to speak publicly.

The official said passengers traveling internationally could see increased screening at gates and when they check bags, as well as other measures on flights such as stowing carryons and personal items before the plane lands.

While air travelers contended with the new rules, investigators tried to determine facts about the suspect's background.

He claimed to have received training and instructions from Al Qaeda operatives in Yemen, a law enforcement official said on the condition of anonymity because the investigation is ongoing.

Rep. Jane Harman, D-Calif., chairman of a House Homeland Security subcommittee, said there were "strong suggestions of a Yemen-al Qaida connection and an intent to blow up the plane over U.S. airspace." Several officials said they have yet to see independent confirmation.

A Virginia-based group that monitors militant messages called attention Saturday to a Dec. 21 video recording from an Al Qaeda operative in Yemen who warned of a looming bombing in the U.S.

IntelCenter said the Al Qaeda member levied that threat last week during a funeral for militants killed during an airstrike in Yemen two days earlier.